Rheological characterization and extrusion of suspensions of natural zeolites

A rheological characterization and extrusion of aqueous suspensions of natural zeolites were carried out in this work. Preparation of suspensions followed similar routes to those used for the colloidal processing of ceramic powders. The suspensions were prepared at different volume fractions (v/v%) ranging from 5 to 61v/v% for a pH value of 7. The suspensions showed a Newtonian behavior for solid contents up to 20v/v% and shear thinning at higher solid loads. For solid contents above 35v/v%, the suspensions exhibited hysteresis and a yield stress that growth exponentially with the solid load. The appearance of a yield stress and its fast growing at relatively low solid concentration, as compared to other type of ceramic suspensions, is attributed to several factors as inter-particle interactions, the presence of relatively large particles and to the influence of their irregular morphology. Also, a breaking stress was measured for solid contents above 35v/v%, which characterizes a failure of the structure of the suspensions after yielding. This breaking stress determines the onset of slip flow of the suspensions, which is interpreted in this work as a signal of good extrusion characteristics. Finally, inexpensive and free of surface defects tubes were obtained from natural zeolites.